Breeding And Annual Changes Of Gonad Development Of Branchiostoma Floridae In Laboratory

An artificial population of Branchiostoma floridae, produced on September 12th, 2011, was observed for growth and development through 3 years. The larvae open mouth about one day post-fertilization at room temperature, and then the first gill slit was formed quickly. In the growth process, the larvae increased gradually their body length and the number of gill slits. The larva at 3-gill-slit stage lasted for 4 to 5 day. Since then, the larva had continued a quick growth. It started to metamorphose around 20 days post-fertilization, when the body length was 3.5 mm with 8 to 10 gill slits. They grew more slowly during the metamorphosis. The metamorphosis was basically finished in 30 days post fertilization, when the body length was about 4.26 mm with 10 to 15 gill slits. After the metamorphosis, the juveniles grow fast whereas the adult grows slowly when the gonad begins to develop. Amphioxus has the ability to grow throughout its life.A F2 population, spawned on July 30,2012, was used to observe for the annual changes of gonad development from November 2012 to November 2014. About 100 individuals were sampled randomly every month and the gonad development status was estimated individually. The spawning was also recored in breeding season. The results showed that the gonad development was asynchronous in the population level. There were about 20% of the amphioxus individual began to develop gonads in early November 2012, but their genders couldn’t be identified correctly at this time. In early December, nearly 4% of individuals could be identified genders based on their gonads. In January, 2013, there were several individual were matured. After that, the proportion of matured individual increased gradually. In early May, the individuals with matured gonad occupied 23%. The spawning occurred firstly in mid May then increased gradually in late May and reached a peak in June and July. After declining to some extent in August, the spawning increased slightly again in September, and ended in late October. In November 2013,35.6% individuals have matured gonads. Later, the proportion with matured gonads increased gradually, and reached to 50% in early February,64.3% in early April,94% in early May. The spawning occurred in early May, and increased in mid May, then reached a peak in June and July. The spawning decreased in August and ended in October 2014. So, B. floridae spawned from May to October. The two-year-old lancelets in the second reproductive cycle had developed gonad faster than the one-year-old ones in the first reproductive cycle, and the spawning of two-year-old lancelets were also larger than that of one-year-old ones. This study presented the growth pattern and the annual regulation in gonad development of Branchiostoma floridae cultured in laboratory, and provided a lot of biological data for the modeling research and artificial reproduction for the lancelet.